Electrical insulated conductor



RUBBER I D-RAW c0770 .50 RELATIVE VAPOR PRESSURE C. S. FULLER ELECTRICALINSULATED CONDUCTOR Filed July 26, 1959 c- TUSSAH SPUIV SILK B-BLEACHEDCOTTON A-REACTION mooucr 0F CELLULOSE AND METHYLOL UREAS FIG. 6 .03

G-REACTION PRODUCT July 7, 1942.

CELLULOSE FIBERS TREATED WITH A RESIN FORMING COMPOUND CONTAINING AMETHYLOL RADICAL Ms a E s s F 0L IH 9 um m. mm #1 MM F- BLEACHED COTTONC. S. FULLER ATTORNEY s H .0 E w DR f. MW 0 r an -wnN UH .NE 0 V 0E an sP "w 05 04 SR n .6 C 5 a 0 M N .U 0 u -2 E c m m M n Patented July 7,1942 ELECTRICAL INSULATED CONDUCTOR Calvin S. Fuller, Chatliam, N. 1.,assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., acorporatlon of New York Application July 26, 1939, SerialNo. 286,508

11 Claims.

This invention relates to electrical structures and more particularly toelectrical insulated conductors.

Textile served conductors have long been employed in electrical systems.A textile serving of cellulose possesses many mechanical and electricalproperties which are particularly adapted for use as insulation onconductors. However, when subjected to a humid atmosphere it absorbsappreciable quantities of water to decrease markedly its insulationresistance. Materials employed as impregnating media for these textilesdo not prevent this water absorption. For example, it has beenheretofore proposed that the textile served on conductors be impregnatedwith a synthetic resin dissolved in an organic solvent. The resin whileproviding a filling between the interstices of the fibers and anover-all cover for the textile does not ultimately improve the resistivecharacteristics of the insulation on the conductors.

An object of this invention is to insulate a conductor with a materialwhich markedly improves its insulation resistance in humid atmospheres.

A more particular object of this invention is to insulate conductorswith textiles which are flame-proof and resistant to light.

In accordance with this invention, a conductor is insulated with amaterial derived from a cellarlosic substance which is markedly improvedin electrical characteristics from the substance from which it wasderived. The insulation resistance of this material is considerablygreater under humid conditions than cellulosic substances whetherimpregnated or unimpregnated. Further, the materials employed forinsulation in accordance with this invention possess flameproofingproperties and are resistant to the detrimental effects of light. Forexample, such materialshave insulation resistance approximating that oftussah silk, and water-resistant characteristics and a power factorconsiderably superior to those -of the cellulosic substances from whichthey are derived. The materials may be produced by the interaction ofcellulose with a water-soluble resin-forming compound comprising amethylol radical. The materials are prepared preferably by theinteraction of cellulose with a water solution of methylol urea.Preferably the insulated conductor is produced by serving a.

conducting core with a cellulosic substance such as cotton textiles. Theserved conductor is then passed through a water solution of a derivativeof urea such as dimethylol urea. The textile is then subjected to heat.The urea derivatives combine with the cellulosic substances to produce acomposition which has markedly greater insulation resistance andsuperior water-resisting characteristics than the cellulosic substancesfrom which it was derived.

A more comprehensive understanding of this invention is obtained byreference to the accompanying drawing in which,

Figs. 1 and 2 are perspective views partly broken away of conductorsconstructed in accordance with this invention;

Fig. 3 is a view of the apparatus employed in the impregnation ofconductors shown in Figs. 1 and 2;

Fig. 4 is a graphic representation of a comparison of the moistureabsorption characteristics of the insulation employed for conductors inaccordance with this invention with other insulating materials;

Fig. 5 shows graphically the power factor of the insulation employed forconductors in accordance with this invention and raw cotton insulation;and

Fig. 6 is another graphic representation which demonstrates the superiorinsulation resistance of the material employed for the insulation ofconductors in accordance with this invention and other substances usedfor like purposes.

In Fig. l a conductor I0, preferably comprising round flexible copper,is served with a cellulosic insulation ll, impregnated with a watersolution of a resin-forming material comprising a methylol radical.Subsequently the impregnated insulation is subjected to heat to form areaction product of the cellulose with the resinforming material.

In Fig. 2 a'flexible conductor 20 is covered with rubber II in amannerwell known in the art. The rubber insulation 2| is served withcellulosic textiles 22 which are treated with a water solution ofresin-forming material comprising a methylol radical, similar to theinsulation ll shown in Fig. 1.

Typical apparatus for the impregnation of the textile served conductorsis shown in Fig. 3.

Cellulosic textile served wire 3| passes from a drum 30 over a guideroll 32, thence over guide rolls 33; and 34, both of which are situatedin a tank 35. The tank 35 contains a water solution 35 of aresin-forming material comprising a methylol radical. From the tank 35the textile served wire passes over a guide roll 31, through an oven 38to a receiving drum 39. An electrical resistance element 40 in the oven38 supplied by a source of current, not shown, provides the necessaryheat energy.

While any water solution of a resin-forming compound comprising amethylol radical, such as a phenol or urea derivative of formaldehyde,or a mixture of such derivatives may be used to effeet the formation ofthe reaction product with cellulose, it is preferred that a mixture ofmono and dimethylol ureas be employed.

If it is desired to produce a wire such as that shown in Fig. 1, inwhich the impregnating media is an aqueous solution of mono anddimethylol ureas, the following procedure may be practised.

Two servings of alkali cooked and bleached cotton washed to neutralityor between pH 6.5 andcpI-I 7.5 are placed on the conductor. Subsequentlyan additional serving of alkali cooked and bleached cotton similar tothe initial serving is wound thereon. The covered wire is then passedthrough a solution of mono and dimethylol ureas contained in the tank35. The solution is prepared by dissolving one mol of urea in 1.2 molsof neutralized formaldehyde in a 40 I per cent aqueous solution. Thesolution is adjusted to a pH value between 8 and 9 with a base such assodium hydroxide and brought to a temperature of 65 C., for a period ofabout two hours. The solution is then diluted with water in a ratio ofone part of solution with onequarter part of water and held in this formuntil used. This solution is suitable for use for a period ofapproximately two weeks. Immediately prior to use a catalyst such asdiethanol amine hydrochloride is added to the solution in a ratio of .3to .6 cc. of a per cent solution in water to 25 cc. of the ureaderivative solution diluted as noted. The amount of catalyst represents0.18 to 0.36 per cent by weight of the total solution. After theinsulated wire is passed through the tank 35 it is heated in the oven 38at a temperature between 150 to 200 C. The resulting insulation of thewire comprises a reaction product of cellulose and mono and dimethylolureas.

A typical example of a preferred method of preparing cotton for theproduction of the methylol reaction products is as follows:

234 grams of cotton are subjected to a 1.5 per cent sodium hydroxidesolution at 50 pounds steam pressure for three hours with circulation.A, gram of Igepon is added to facilitate wetting out. The cotton iswashed with water until alkali-free and bleached for two hours at 25 C.in 5 liters of water containing 4.6 grams calcium hypochlorite. Thebleached cotton is washed with water, treated for one hour in 4 litersof water containing 1 gram of sodium bisulfite (NaI-lSOa) washed wellwith water and dried rapidly at 80 C.

An alternative method of preparing a cellulose derivative containing amethylol linkage for electrical conductors is as follows:

Alkali cooked and bleached 60/1 cotton is subjected in skein form toimpregnation with a water solution containing 40 grams of mixedmonomethylol and dimethylol ureas in cc. of solution in the presence of0.1 gram of diethanolamine sulphate. The wet skeins are centrifuged tobelow fiber saturation, dried at 50 C., and subjected to C. for fifteenminutes. This product is then served on a electrical conductor as aninsulating covering.

Alternatively, the skeins after drying at 50 C. are served directly onthe conductor and subsequently cured in place by passing the servedconductor in a continuous manner through a heated chamber C.) at a speedof 56 feet per minute or the reaction product is formed by heating theserved wire after drying at 50 C. in the form of an open coil in an ovenat 150 C. for ope-half hour.

For certain purposes, it is desirable to insulate a conductor with acellulosic substance and treat the material with a water-solubleresinforming compound comprising-a methylol radical such as a watersolution of a methylol urea or a methylol phenol or a mixture of amethylol urea and a methylol phenol so that not only does the compoundreact with the cellulosic substance but in addition the resinsubstantially fills the pores and interstices of the substance. Foraccomplishing this result, the cellulosic substances may be impregnatedin a water solution of the resin-forming compound and the amount ofcompound which is normally removed by dies may be regulated so that anappreciable amount will remain within the pores and interstices of thesubstance. Subsequently the conductor may be heat treated to form thereaction product of cellulose and the methylol compound and to cure thesurplus resin in the pores and interstices of the substance. Forexample, a copper conducting core may first be served with cottontextiles and the servingimpregnated with a methylol derivative of urea.After subjection to heat, a second serving of cotton textiles may beapplied to the insulated conductor. The served conductor may beimpregnated in the water solution of the methylol derivative of urea andsub,- sequently subjected to heat treatment. The amount of compoundremaining on the cellulosic substance after each impregnation in thecompound but before heat treatment may be regulated by adjustment of thewiping dies so that in addition to effecting the formation of thereaction product of cellulose and the watersoluble resin, the pores ofthe textile are substantially filled by the cured form of the compound.

When a cellulosic material is treated with a water-soluble ureaderivative, a reaction product is formed which is markedly differentfrom that of the cellulosic material from which it was derived. Forexample, on heating demethylol urea with cellulose, the dimethylol ureamelts both in the pores and on the surface of the fibers, and severalreactions occur. In the first place, the dimethylol urea can condensewith itself to form a resinous compound with the splitting oif of waterand formaldehyde. One course of such a reaction is illustrated in thefollowing equation:

NH-CHzOH HN-CHz- N-CH2 -NCH:OH

] heat (lJ C=O :0 =0 =0 0 I catalyst NH-CHzOH Simultaneous with thisreaction, however, the following ones involving cellulose occur:

H\ Boomon no-on H OH Glucose unit of cellulose dimethylol urea HzO I (2)or with two glucose units +2Hz0 I (3) In reaction (2)- for convenienceonly one glucose unit of the cellulose has been represented' Acombination between two cellulose hydroxyls with dimethylol urea throughan acetal type reaction is postulated. In this case the reaction ispictured as intramolecular and a cyclic structure results. Instead ofbridging the 2, 3 hydroxyl groups of glucose, the dimethylol urea maybridge the hydroxyls of the 2,5 or the 3,5 positions. Also it ispossible that hydroxyl groups of adjacent glucose units in the samecellulose chain may be bridged. It is realized, of course, that in placeof dimethylol urea higher methylol compounds, like the products in (1),may react similarly.

In reaction (3) the same type of combination is shown asoccurring-intermolecularly instead of within the same molecule. In thiscase, as in the previous one, the final result is to reduce the totalnumber of OH groups present in the final compounds.

A further reaction which may occur to some extent is one betweenformaldehyde given 011 in (1) and the cellulose hydroxyls with theproduction of a formal as shown in (4). Here again other pairs of thecellulose hydroxyls may be involved. The extent of this reaction,however, is no doubt rather small.

Fig. 4 shows graphically the water absorption of the reaction productsof dimethylol urea and cellulose, tussah spun silk and bleached cotton.Curve A indicates the water absorption characteristics of the reactionproduct of dimethylol urea and alkali cooked and bleached cottontextiles; curve B the same characteristics of bleached cotton; whilecurve C shows the properties of tussah silk. It is observed that thereaction product absorbs materially less water at all humldities thaneither tussah silk or the bleached cotton from which the reactionproduct is derived.

Fig. 5 shows the correlation of power factor and temperature of rawcotton and the reaction product of methylol urea and cotton. Curve Drepresents graphically the power factor at various temperatures of rawcotton and curve E shows the same characteristics of reaction product ofcellulose and methylol ureas. The reaction product has a considerablylower power factor than that of the cotton from which it i derived. Thefollowing table shows the'values of the power factor maxima for thesetwo materials at various frequencies in the dry condition:

Power factor maxima In Fig. 6 the insulation resistance of cotton,tussah silk and the reaction product under variousconditions ofhumidityis shown. The insulation resistance of bleached cotton indicatedby curve F is plotted on a logarithmic scale against relative humidity.The insulation resistance of the reaction product to the humidconditions appears as curve G, while that of tussah silk is shown bycurve H. These curves indicate clearly the superior nature of theinsulation comprising the reaction product over raw cotton and tussahsilk.

The efiect of concentration of the resins employed for impregnating thetextiles on the nature of the reaction product as revealed by theinsulation resistance of the product resulting from the interaction ofresin and cotton yarn on cotton served wire is demonstrated by an examination of the following table. The cotton served wires were impregnatedas heretofore described. The original solution employed for thisimpregnation contained 60 per cent of methylol ureas by weight.

Insulation resistance 38 0., relative humidity Pts. of water by volumeto one pt. of solution Kilomegohms g ;337

gig bleached cotton-served cotton #22 AWG wire 0.00 0.16. 223, 000-340,000 0.25. 210, 000-340, 000 378-1174 0.33. 120, 000-223, 000 0.50. 71,000-120, 000 350-765 0.66.. 34, 000-103,000 0.75. 22, 000-58, 000 1.00.18, 000-38, 000 193- 397 2.00. 35. 3-03. 6 6.00. 5. 40-11. 7 Washedcotton 1 Tussah s1 2, 500-16, 000 2-60/1, /2 alkali cooked bleachedcotton on #22 AWG wire 0. 40-1. 00 2-62/1 tussah silk and 1-40/2 washedcotton on #22 AWG wire 2. 003. 00

In the first column of the table the parts of water by volume added toone part of the original solution containing 60 per cent by weight ofmethylol ureas are noted. The insulation resistance of the bleachedcotton per three-quarter inch length of a No. 60 single thread which isimpregnated with the solution and heat treated as heretofore describedfor the various solutions is tabulated in the second column, while thatof conductors served with cotton and treated with the solutions appearin the third column. It is observed that as the concentration of resinis decreased there is a definite drop in the insulation resistance. A 60per cent water solution of methylol ureas appears to be the mostdesirable for the impregnation of the textile served conductors. Theoptimum for a particular purpose can be ascertained empirically.

An interesting experiment illustrates the differences between thesunlight resisting characteristics of cotton and the reaction products.Two samples of wire served with the same cotton textile, one of whichwas treated with a mixture of monomethylol and dimethylol ureas, to formthe reaction product in accordance with this invention and the other ofwhich was untreated, were subjected to identical weathering tests for aperiod of over a year. At the end of this time both were examined fordeterioration. The cotton on the untreated sample was badly tendered andreadily crumbled on slight abrasion, whereas that of the reactionproduct had retained practically its original tensile strength andabrasive qualities. The insulated conductors in accordance with thisinvention are, therefore, admirably adapted for use on wires exposed tothe elements.

The reaction product for the insulation of conductors is formed by theinteraction of all types of water-soluble urea resins containing amethylol linkage. For example, water-soluble thio urea resins havingmethylol linkages likewise react with the cellulose insulation under theconditions outlined to produce a reaction product superior from aninsulation resistance, water resistance and abrasive resistancestandpoint to the original cellulosic material from which it wasderived. Then, too, other types of cellulosic materials than cottontextiles ma be used, such as paper pulp. Preferably, however, thecellulosic material is first placed on the wire before the reactionproduct is formed. v

A typical example of the preparation of other methylol derivatives ofcellulose, such as the reaction product of cellulose and methylolphenols, which may be employed for the insulation of conductors is asfollows:

188 grams of phenol is reacted at 100 C. wit 200 cc. :of 40 per centformalin in the presence of 4 cc. concentrated ammonia water for one anda half hours. The resulting solution comprising mono and dimethylolphenols is employed to react with purified cotton. An electricalconductor containing one serving of 40/2 cotton. and two outer servingsof 60/1 cotton previously purifled is drawn continuously through thesolution and the excess removed by wiping with rubber or felt. The wireis then passed through a hot air chamber where it is dried and heated tocause resin formation and compound formation with the cellulose. Atemperature of 180 C. and a speed of 56 feet per minute is preferablyemployed.

compounds is shown by the following electrical results:

Another example of a reaction product of cellulose and a resin-formingcompound having a methylol linkage is as follows: 282 grams of phenoland 180 grams of urea are reacted with 540 cc. of formalin (40 per cent)in the presence of 30 cc. of N/5 sodium hydroxide for two hours at 65 C.The resulting solution is diluted with 240 cc. of water and employed fortreating cotton served wire as described in the previous example. Themixed methylol ureas and methylol phenols combine with the cellulose.The insulation resistance of insulated wire before and after treatmentat 38 C. and per cent relative humidity is:

Megohms per 19 in. length Triple cotton served #22 AWG wire-no treatmentTriple cotton served #22 AWG wiretreated 510.00

Alternatively, both the methylol phenols and the mixed methylol ureasand phenols can, of course, be applied directly to the cotton celluloseand then served on wire, curing being accomplished either before orafter serving.

The stability of the resin cellulose compounds of this invention is bestdemonstrated by an examination of the results of tests conducted on aninsulated wire prepared by employing mixed methylol ureas and-methylolphenols as heretofore described. One sample was placed in an atmosphereof per cent relative humidity for one week, then dried over CaCl: oneweek, then placed in an atmosphere of 75 per cent relative humidity forone week, then dried one week. This sequence was repeated for one year.At the end of this time the insulation resistance of the wire at 38 C.,85 per cent relative humidity was still 220 megohms, i. e., 1500 timesthat of the original untreated wire. A second sample was placed on theroof exposed to sunlight. At the end of one year and four months theinsulation resistance of this wire was still over 80 times that oftheoriginal untreated sample.

This invention embraces within its scope the insulation of conductorswith any reaction product of cellulose and a resin-forming materialcomprising a methylol radical. For example, cellulosic materials for theinsulation of wire may be treated with water-soluble amino compoundsother than urea, such as water-soluble methylol derivatives ofdicyandiamide with a potentially acid-forming catalyst such as ammoniumchloride. Or water-soluble methylol derivatives of melamine(2,4,6-triamino-s-triazine), of guanidine or guanidine carbonate may be'used in a manner similar to that heretofore described. Likewise, otherphenolic types of compounds may be employed such as water-solublemethylol derivatives of resorcinol, pyrocatechol, phloro glucinol,pyrogallol and the like. Among other examples are the methylolderivatives of ketones. Thus, four parts of acetone may be mixed withtwo parts of water and three parts of formalin (40 per cent) by volume.Five cc. of 10 per cent sodium hydroxide is added as a catalyst. AfterKilo megohms per A," length Untreated 90 Treated 1700 Obviously themethylol derivatives of other ketones than acetone may also be employed,such as p-methyl-F-keto butonol or ,S-methyl ,B-hydroxy methy I-ketobutonol derived from the reaction of formalin and methyl ethyl ketone.

Preferably acid catalysts are employed in the curing reaction except inthe case of methylol phenols and methylol acetone. For the formation ofthe reaction product of cellulosic material and these latter substances,alkaline catalysts may be used.

This invention also includes within its scope the multiple treatments onthe same cellulosic base material with the same or differentwatersoluble resin-forming compounds comprising a methylol radical.Successive treatments and cures may be made by employing the samemethylol derivative or different methylol derivatives may be appliedsuccessively as well as simultaneously. For example, a water-solublemethylol urea may be applied to an electrical conductor having acellulosic material thereon. After heating to effect the formation of areaction product of the cellulose and methylol urea, a water-solublemethylol phenol is applied and heated in a manner similar to thatheretofore described to produce a reaction product of cellulose and themethylol phenol. In certain cases, particularly when alkaline catalystsare employed, it may be desirable to wash the final product and to dryafter the washing.

While preferred embodiments of this invention have been illustrated anddescribed, various modifications may be made therein without departingfrom the scope of the appended claims.

What is claimed is: 1. An insulated electric conductor comprising aconducting wire covered with a layer of insulation comprising a fibrousreaction product of cellulose and a water-soluble resin-forming compoundcontaining a methylol radical, made by partially reacting fibrouscellulose material, by impregnation and heating, with an aqueoussolution of a water-soluble resin-forming compound containing a methylolradical so that the identity of the fibers of the original cellulosematerial is retained and the fibrous reaction product is a cellulosederivative which is predominantly cellulosic in nature, but which hasflame resistance, abrasion resistance, moisture resistance, lightresistance, and power factor charac teristics greatly superior to thoseof the original cellulose material, and electrical resistivities at highand low humidities greatly superior to those of the original cellulosicmaterial and approximating those of silk.

2. An insulated electric conductor comprising a conducting wire coveredwith a layer of insulation comprising a fibrous reaction product ofcellulose and a water-soluble resin-forming compound containing amethylol radical, made by partially reacting fibrous cellulose material,by impregnation and heating, with an aqueous slution of a water-solubleresin-forming compound containing a methylol radical so that theidentity of the fibers of the original cellulose material is retainedand the fibrous reaction product is a cellulose derivative which ispredominantly cellulosic in nature, but which has flame resistance,abrasion resistance, moisture resistance, light resistance, and powerfactor characteristics greatly superior to those of the originalcellulose material, and electrical resistivities at high and lowhumidities greatly superior to those of the original cellulose materialand approximating those of silk, the pores of said fibrous reactionproduct and the interstices between the fibers thereof beingsubstantially completely filled with a resin produced by curing awater-soluble resin-forming compound containing a methylol radical.

3. The method of manufacturing an electrical conductor comprisingapplying a fibrous cellulosic material to a conducting core, passingsaid core through a water solution including a potentially acidsubstance and a water-soluble methylol derivative of urea, removing theexcess of said solution, drying said conductor and heating saidconductor between C. to 200 C.

4. An insulated electrical conductor comprising a conducting wirecovered with a layer of insulation comprising a fibrous reaction productof cellulose and a water-soluble mixture of monomethylol urea anddimethylol urea, made by partially reacting fibrous cellulose material,by impregnation and heating, with an aqueous solution of a mixture ofmonomethylol urea and dimethylol urea so that the identity of the fibersof the original'cellulose material is retained and the-fibrous reactionproduct is a cellulose derivative which is predominantly cellulosic innature, but which has flame resistance, abrasion resistance, moistureresistance, light resistance, and power factor characteristics greatlysuperior to those of the original cellulose material, and electricalresistivities at high and low humidities greatly superior to those ofthe original cellulosic material and approximating those of silk.

5. An insulated electrical conductor comprising a conducting wirecovered with a layer of insulation comprising a fibrous cellulosicreaction product of fibrous cotton and a product obtained by heatingurea and formaldehyde in the pres ence of water, said cellulosicreaction product being formed by partially reacting fibrous cotton, byimpregnation and heating, with an aqueous solution of saidurea-formaldehyde product so that the identity of the fibers of thecotton is retained and the fibrous cellulosic reaction product is acellulose derivative which is predominantly cellulosic in nature, butwhich has flame resistance, abrasion resistance, moisture resistance,light resistance, and power factor characteristics greatl superior tothose of the original cotton, and electrical resistivities at high andlow humidities greatly superior to those of cotton and approximatingthose of silk.

6. An electrical conductor comprising a conducting member covered with alayer of cellulosic fibrous material in which the cellulose has beenpartially chemically transformed by' impregnation with an aqueoussolution of a watersoluble resin-forming compound containing a methylolderivative of urea and by subsequent heating to cause a partial chemicalcombination of the cellulose fibers with the impregnant as evidenced byincreased electrical resistivity of the fibers at high humidity.

'7. The method 01 treating an electrical conducting wire covered with alayer of fibrous cellulose material comprising impregnating saidfibrous-cellulose material with an aqueous solution of a water-solubleresin-forming compound containing a methylol radical and heating saidimpregnated cellulose material so that said resini'orming compoundpartially reacts with said cellulose material, without destroying theidentity of the fibers of said cellulose material, to form a fibrousreaction product which is a predominantly cellulosic cellulosederivative but which has flame resistance, abrasion resistance, moistureresistance, light resistance, and power factor characteristics greatlysuperior to those of the original cellulose material, and electricalresistivities at high and low humidities greatly superior to those ofthe original cellulose material and approximating those of silk.

8. An electrical conductor comprising a conducting member covered with alayer of cellulosic fibrous material in which the cellulose has beenpartially chemically transformed by impregnation with an aqueoussolution of a water-soluble resin-iorming compound containing a methylolderivative of phenol and by subsequent heating to cause a partialchemical combination of the cellulose fibers with the impregnant asevidenced by increased electrical resistivity of the fibers at highhumidity.

9. An electrical conductor comprising a conducting member covered with alayer or cellulosic fibrous material in which the cellulose has beenpartially chemically transformed by impregnation with an aqueoussolution of a water-soluble resin-forming compound containing a mixtureof a methylol derivative of urea and a methylol derivative of phenol andby subsequent heating to cause a partial chemical combination of thecellulose fibers with the impregnant as evidenced by increasedelectrical resistivity of the fibers at high humidity.

10. An electrical conductor comprising a conducting member covered witha layer of cellulosic fibrous material in which the cellulose has beenpartially chemically transformed by impregnation with an aqueoussolution of a methylol derivative of a ketone and by subsequent heatingto cause a partial chemical combination of the cellulose fibers with theimpregnant as evidenced by increased electrical resistivity of thefibers at high humidity.

11. An electrical conductor comprising a conducting member covered witha layer of material comprising cellulose textile fibers which have beenpartially chemically reacted with an aqueous solution of a methylolderivative of urea as evidenced by increased electrical resistivity at Ihigh humidity and by greater resistance to disintegration upon exposureto the atmosphere, the

pores of said fibers and the interstices between

